A surface discharge type PDP that is used for a color display has partitions for preventing discharge interference between neighboring cells. There are two partition arrangement patterns. One is a stripe pattern in which a display area is divided into columns of a matrix display, and another is a mesh pattern in which the display area is divided into cells. When the stripe pattern is adopted, a plurality of partitions, each of which having a band-like shape in a plan view, is arranged in the display area. When the mesh pattern is adopted, a partition (a so-called box rib) having a shape surrounding each cell in a plan view is arranged in the display area.
In general, a partition is a baked material of low melting point glass and is formed by using a sandblasting method. FIG. 12 shows the conventional process of forming a partition. The partition pattern shown in FIG. 12 is a stripe pattern. The partition is formed by the following steps. (A) Paste of low melting point glass is applied to a surface of a glass substrate 101 at a uniform thickness and is dried. Then, a sheet-like partition material 102a made of the dried paste is covered with a photo-sensitive resist film 103a that is a masking material. (B) A photolithography technique including exposure of the pattern and development of the same is used for forming masks 103 of a pattern corresponding to the partition. (C) A cutting material is blown to cut portions of the partition material 102a that are not masked. In this process, a spray nozzle is moved in a reciprocating manner along the longitudinal direction of the bands of the mask pattern, so that the wide area of the partition material 102a is dug down equally and gradually. (D) The masks 103 that are remained on the patterned partition material 102b are removed. (E) The partition material 102b is baked so that a partition 112 is obtained. In the baking process, the volume of the partition material 102b is reduced due to dissipation of binder.
As shown in FIG. 12(C) of the sandblasting step, the partition material 102b is scooped out under the mask 103 at ends of the mask 103 in the direction along the movement of the nozzle so that side cuts are formed. This is caused by that a part of the cutting material ejected from the nozzle is reflected by the glass substrate 101, meets the cutting material ejected from the nozzle, and has a moving component in parallel with the direction of the nozzle movement so that the cutting material having the components scoop out the ends of the partitions. Quantity of the side cuts becomes greater as a cutting speed increases. It is considered to be the reason that a ratio of the above-mentioned component increases when quantity of a cutting material ejected per unit time is increased. Hereinafter, the above-mentioned component that causes the side cut is referred to as a jet. This side cut induces mask exfoliation that is a cause of a pattering deficiency during the cutting stage. In addition, the side cut prevents the partition 112 from being formed in uniform height. When the partition material 102b having curved edges as shown in FIG. 12(D) is baked, the edge portions of the partition 112 become higher than other portions as shown in FIG. 12(E). More specifically, concerning a partition having a design value of height of 140 μm, it has a height of approximately 200 μm before the baking process. After being baked the height is reduced to approximately 70%, and the edge portions become higher than the other portions by 30 μm. This phenomenon is called a “projection”, and it is caused by that the top portion is free while the bottom portion is restrained from contracting since it is stuck to the glass substrate 101. The projection causes insufficient contact between substrates in a PDP assembling process in which a substrate having the partition 112 is put together with another substrate. If the PDP has a gap between the surfaces to contact with each other, the substrates may vibrate locally due to electrostatic attraction when a high frequency driving voltage is applied for a display, resulting in slight operation sound (buzz sound).
Studying about the relationship between the phenomenon and the quantity of the projection of each portion in the panel, it is found that this phenomenon is prevented by reducing the quantity of the projection to a half of the current value, i.e., 16 μm or less, preferably 12 μm or less considering variation in the manufacturing process.
An object of the present invention is to provide a method for forming partitions of the exact pattern and height as designed in a display area without generating any projections that can be obstacles to contact between substrates.